Typically, while transferring a document, an image reading apparatus such as a scanner captures an image of the document, using an image capturing device such as a line sensor with imaging elements arranged one-dimensionally. For this reason, a foreign object such as paper powder, dust and paste, etc., attached to a glass surface of the image capturing device may cause vertical stripe noise to appear on a document image acquired by capturing the document.
A copying machine including a CIS having its reading surface coated to prevent reading vertical stripes generated as a paste-like foreign object attached to a document adheres to the reading surface is disclosed. The copying machine detects the thickness of the document and adjusts the gap between the glass surface of the CIS and the roller portion of a reading roller in accordance with the detection result (see patent literature 1).